Standard DIN EN 228 stipulates the minimum requirements for the characteristic values and properties for non-leaded types of gasoline. Table 1 shows an excerpt of the essential characteristic values for fuel.
TABLE 1Requirements accordingto DIN EN 228Characteristic valueUnitSuperPlusSuperNormalDensity at 15° C.Kg/m3720-775Knock resistanceR.O.N.min. 98min. 95min. 91  M.O.N.min. 88min. 85min. 82.5Lead contentmg/Lmax. 5  Distillation range*% (V/V)Evaporated quantity(Class A)at 70° C., E7020-48at 100° C., E10046-71at 150° C., E150  min. 75Evaporated quantity(Class D/D1)at 70° C., E7022-50at 100° C., E10046-71at 150° C., E150  min. 75Final boiling point (FBP) ° C. max. 210(Class A/D/D1)Volatility indicator VLI**(VLI = 10 × VP + 7/E70)Class D1Index  max. 1150Distillation residue% (V/V)max. 2Vapor pressure (DVPE)kPaClass A45.0-60.0Class D/D160.0-90.0Evaporation residuemg/100 mLmax. 5Benzene content% (V/V)max. 1Sulphur contentmg/kg max. 150Oxidation stabilitymin max. 360Copper corrosionExtent ofmax. 1corrosion*Class A: May 1-September 30 (summer)Class D: November 16-March 15 (winter)Class D1: March 16-April 30 & October 1-November 15 (transition)**Vapor Lock Index
Especially important in all of this is knock resistance which is described with two characteristic numbers: the motor octane number (M.O.N.) and the research octane number (R.O.N.). Briefly, knocking can occur during combustion in any gasoline engine and cause extensive engine damage, if intense enough. For this reason, engine developers are required to prevent the non-uniform combustion that occurs during knocking. In other words, they must integrate knock control systems into engine controls and to proactively prepare the engine for the fuel's knock resistance. High octane numbers permit higher performance with a simultaneously higher degree of efficiency of the engine and, therefore, lower consumption. For these reasons, higher prices can also be fetched with higher-octane fuels, even though they have almost the same energy content (fuel value) as lower-octane fuels.
The worldwide determination of octane numbers is nowadays carried out empirically and according to standardized processes in the fuel producers' laboratories. Special one-cylinder test engines with a variable compression ratio that can be adjusted to the respective fuel quality are used for this purpose. The objective is to compare the knock intensity of the fuel being tested with fuels of a known octane number in order to determine its octane number. Interpolation between octane numbers may be necessary. The standard arbitrarily assigned octane number for isooctane is 100 and for n-heptane is 0. By mixing these components, a fuel can be produced that will have the same knock intensity as the fuel being tested. The octane number that is being determined for will then correspond to the volumetric share of isooctane in the fuel mixture. Only testing conditions differentiate between M.O.N. and R.O.N. All other process steps are the same and the same measuring techniques and test engine were used.
The degree of knock intensity is measured with an electric sensor (electronic detonation meter) attached to the engine's combustion chamber (FIG. 1) and an indicator (knock meter) displays the result. The knock intensity and frequency calculations are not performed with the measuring data, however. Research has shown that fuels with equal octane numbers can actually have a different knock behavior regarding intensity and frequency. If this method is professionally applied with the corresponding experience, an accuracy of no more than +0.2 octane numbers can be achieved. The operation is done manually and takes between 20 and 30 minutes per octane number. There have been—and still are—many attempts to determine the octane number with calculations or another instrument—i.e., outside the engine. Unfortunately, so far it has not been possible to achieve this with the desired accuracy. If the fuel composition is known, a gas chromatography analysis or infrared spectroscopy can give reasonably accurate results, but these methods are only used in refineries because they know exactly the composition of their fuel. A fundamental improvement of the device and method has not yet been found.
The following problems have been detected in assessing the valid processes for determining the octane number:
The accuracy of the process can be improved upon.
The process is time-consuming; it cannot be automated and allows no online indication.
In the process, the knock intensity is indicated directly after the analog processing of the measuring signal. No exact calculation of the knock intensity and frequency takes place.
Whether the determined octane numbers actually reflect the knocking resistance of the fuels that current combustion engines require has been called into question.
It is, therefore, an object of the invention to create a process that will provide a fast and reliable characterization of the knock resistance of fuels possible.